Device and method for assigning a tool to a workpiece

ABSTRACT

For assigning a tool to a workpiece conveyed on an assembly line, at least one transmitter is arranged in the area of an assembly line, and a receiver is arranged on the tool. An analyzing unit determines the distance of the tool from each transmitter, based on the transit times of at least one received signal, and an indicating device emits positions information regarding workpieces on the assembly line. An assignment unit assigns a tool or a tool position to a workpiece, based on at least one distance of the tool from the transmitter, and on the workpiece positions. The arrangement of the transmitters and receivers can also be interchanged.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German patent document 199 55646, filed 19 Nov. 1999 (PCT International Application No.PCT/EP00/11186, filed 11 Nov. 1999), the disclosure of which isexpressly incorporated by reference herein.

The invention relates to a method and apparatus for assigning a tool toa workpiece on an assembly line.

In the assembly line production of workpieces, tools operated by workerscan only rarely be assigned to a certain part to be worked. Inparticular, it is impossible to determine where a tool is situated withrespect to a workpiece located on an assembly line. Thus, it couldhappen, for example, that workpieces, such as vehicles, leave theassembly without the certain screwed connections. Checking is not easilyperformed.

It is an object of the present invention to provide a method andapparatus which permit the assignment of tools to a workpiece conveyedon an assembly line.

This and other objects and advantages are achieved by the method andapparatus according to the invention, in which the position of a tool isdetected either relative to a workpiece or relative to a stationarysystem of coordinates and is assigned to a workpiece situated on theassembly line. In this case, an identifier (for example, a production orchassis number) is assigned to each workpiece, and the position of thetool is detected by analysis of the transit times of signals emitted bya transmitter and received by a receiver. The position of the tool canbe computed by way of trigonometric functions. According to anembodiment, a transmitter or a receiver is arranged on the tool. Thearrangement of a receiver on a tool has the advantage that disturbancescaused by the tool operation have a less interfering influence.Depending on whether a transmitter or a receiver is arranged on thetool, the pertaining counterparts (the receivers or the transmitters)are provided in the area of the assembly line.

According to a preferred embodiment, the receivers or transmitters notarranged on the tool are stationary in space. As a result of theanalysis of the transit times between the transmitters and the assignedreceivers, the absolute position of the tool can be indicated in thespace.

In the case of a tool which is movable in all direction, threetransmitters (or alternatively, three receivers) are required in orderto achieve an unambiguous localization in space. However, when the toolis movable in only one defined direction with respect to the vehicle, asingle transmitter (or alternatively construction, a single receiver)may be sufficient.

According to another embodiment, a transmitter (alternatively areceiver) can also be moved along on the assembly line, for example,together With a certain workpiece, so that, by distance measurement,information can already be derived with respect to the distance of thetool from the transmitter (alternatively, the receiver) arranged on theworkpiece.

By means of the already existing knowledge of identifiable workpieces onthe assembly line and their known momentary positions, a time-relatedassignment of a tool to a workpiece can be made from the position of thereceiver (alternatively, the transmitter) arranged on the tool.According to the detection rate of the tool position, preciseinformation can therefore be obtained as to whether the tool has beenguided to a particular position of a workpiece that has a knownidentification. By storing these data, an overall check is possible asto whether a tool has been guided to a workpiece.

The method and apparatus according to the invention can basically beused for all tools for which the assignment to a workpiece is important.On the whole, the present invention is less expensive and can be used ina more flexible manner than known mechanical devices.

According to an advantageous embodiment, ultrasonic devices can be usedas the transmitters and receivers. The transmitters can emit graduallytriggered signals; or as an alternative, each transmitter emitscharacteristic signals. The emitted signals are received by thereceiving unit and are assigned to the corresponding transmitters. Fromthe transit times of the signals, the distances can then be computedbetween the respective transmitters and receivers and the position ofthe tool can be determined in this manner.

As mentioned above, when at least three transmitters (alternatively,three receivers) are used, an unambiguous position determination can bemade also in the case of a tool which is freely movable. In this case, azero point can be determined and the position of the tool can beindicated with respect to this zero point.

For checking the assembling progress, it is advantageous for the datafor the assignment of a tool to a vehicle supplied by an assignment unitto be stored in a memory, particularly a non-volatile memory. The datacan also be received in a memory medium to be stored, so that theassembling progress can be precisely checked for an extended timeperiod.

According to a preferred embodiment, it is also detected and recordedwhether the tool (for example, an electric screwdriver), has beenoperated according to its function. Thus, not only can the guiding ofthe tool to a certain vehicle be reconstructed, but also its properfunctional operation at a certain point. For example, in the case of anelectric screwdriver, it can be determined by way of the applied torquewhether the screwed connection was carried out correctly. When theelectric screwdriver is operated without applying the latter to thescrew or when a screw is twisted off, no expected torque will occur sothat no proper screwed connection on a defined identifiable workpiececan be reported. Such feedback of properly implemented working steps cantake place in the case of all operable tools and can, in turn, beassigned to workpieces.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of vehicles arranged on an assemblyline with respect to a receiver arranged on a tool, the position of thereceiver being determined by means of transmitters;

FIG. 2 is an electric wiring diagram for such a system according to theinvention; and

FIG. 3 is another schematic representation of vehicles arranged on anassembly line with respect to a transmitter arranged on a tool, theposition of the transmitter being determined by receivers.

DETAILED DESCRIPTION OF THE DRAWINGS

Although the invention will be now described in the context of assemblyof a vehicle. The method according to the invention can also be used forall other workpieces which are identifiable and are transported on anassembly line.

FIG. 1 is a schematic view of an assembly line B on which variousunambiguously identifiable vehicles (in this case, two) A₁ and A₂ aremoved in the direction of the arrow P. A vehicle position F₁ and F₂respectively is assigned to each vehicle A₁ and A₂. In this case, eachvehicle position of a just assembled vehicle is known in a controlmaster system. These, positions can be indicated in a defined system ofcoordinates 10.

The vehicle position can be determined, for example, as follows. When avehicle A₁ is placed on the assembly line B, its chassis number is readinto the control master system by means of a transponder. By monitoringthe advancing of the assembly line it can always be determined where onthe assembly line a particular vehicle is located at a particular time.

In the area of the assembly line B, a tool is provided, in this case, anelectric screwdriver (not shown in detail), on which an ultrasonicreceiver E is arranged. The receiver E receives signals from ultrasonictransmitters S1, S2 and S3 which are stationarily mounted in theassembly bay. By way of the different transit times analyzed by acircuit to be explained later, the distances L1, L2 and L3 aredetermined between the receiver, on the one hand, and the assignedtransmitters S1, S2 and S3, on the other hand. From these distances L1,L2 and L3 and the positions of the transmitters S1, S2 and S3, thecoordinates of the receiver (Xε, Yε, Zε) with respect to a defined zeropoint N can be computed as a whole.

FIG. 2 is a schematic wiring diagram of the above-described systemaccording to the invention. The transmitters S1, S2 and S3 emitgradually triggered ultrasonic signals which are detected by thereceiver E. An analyzing unit 20 is connected with the transmitters S1,S2 and S3, and with the receiver E; based on the different transit timesand the known positions of the transmitters, it can determine thelocation of the receiver in the assembly bay. This location is fed to anassignment unit 40, which also receives from an indicating device 30,the various positions F₁ and F₂ of vehicles A₁ and A₂ situated on theassembly line B. By comparing the individual positions, a tool or a toolposition can be assigned to an identified vehicle.

FIG. 3 shows an alternative variant to that of FIGS. 1 and 2. Here, thearrangement of transmitters and receivers is interchanged. An assemblyline B′ is again schematically shown, on which the differentunambiguously identifiable vehicles A₁′, A₂′, A₃′, A₄′, A₅′ and A₆′ aresituated. The assembly line B′ is moved in the direction of the arrowP′. A vehicle position F₁′ to F₆′ is assigned to each vehicle A₁′ toA₆′. When the vehicles A₁′ to A₆′ are placed, each emits a vehicleidentification to a receiving apparatus EM by way of a transponder,which receiving apparatus EM transmits this information to a computer50. By way of an assembly line movement detection device 60, which isalso connected with the computer, the assembly line movement is known sothat each vehicle position can be reconstructed on the assembly line B′,and indicated relative to a defined system of coordinates.

In the area of the assembly line B′, two tools 70, 70′, (in this case,two electric screwdrivers), are provided, each having a respectivetransmitter S′, S″. The transmitters S′, S″ again are ultrasonictransmitters whose signals are received by ultrasonic receivers E1′, E2′and E3′ stationarily mounted in the assembly bay. Based on the differenttransit times, the distances between the transmitters S′, S″, on the onehand, and the receivers E1′, E2′ and E3′, on the other hand, aredetermined. In turn, from these distances and the positions of thereceivers E1′, E2′ and E3′, the coordinates of the transmitters can becomputed with respect to a defined zero point.

According to FIG. 3, the transmitters S′ and S″ and the receivers E1′,E2′, E3′ emit their signals to the computer 50 which centrally comprisesthe analyzing unit, the indicating unit and the assignment unitseparately illustrated in FIG. 2. The assignment of the tools 70 and 70′to the individual vehicles takes place analogous to the description inFIGS. 1 and 2. In the present case, the position of the tool and thepositions of the vehicles F1′ to F6′ are compared with one another, anda tool 70, 70′ is assigned to a certain vehicle if the distances arewithin defined ranges ST1, ST2.

By continuously detecting of the tool position, the guiding of a tool toa vehicle can be reconstructed and checked. Also, if the functionallyproper tool operation, for example the proper operation of the electricscrewdriver, is detected, in addition to the guiding of the tool to thevehicle, the implementation of a certain assembly operation on anidentified vehicle can also be recorded. Thus, it can be checked in asimple manner whether all screwed connections to be carried out by meansof an electric screwdriver were correctly finished. If a vehicle thenleaves the assembly line without the implementation of the requiredscrewed connections on this vehicle, a special indication can takeplace. All data can also be filed in a memory, for example, that of thecomputer 50.

The above described method according to the invention can of course beused not only in the assembly of vehicles, but also in the case of allworkpieces to be assembled. In this case, all other tools can also beused.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. Apparatus for assigning a tool to a workpiece conveyed on an assemblyline, comprising: at least one transmitter arranged in the area of anassembly line; a receiver arranged on the tool; an analyzing unit whichdetermines a position of the tool relative to a defined fixed referencepoint, based on transit times of signals transmitted by said at leastone transmitter and received by said receiver; a device which indicatespositions of workpieces conveyed on the assembly line, relative to theassembly line; and an assignment unit which assigns a tool or a toolposition to a particular workpiece, based on a comparison of thedetermined position of the tool and the workpiece positions indicated bythe indicating device.
 2. The apparatus according to claim 1, wherein:said at least one transmitter comprises a plurality of stationarytransmitters, and positions of the transmitters are known.
 3. Theapparatus according to claim 1, wherein at least one transmitter movesalong with an assigned workpiece on the assembly line.
 4. The apparatusaccording to claim 1, wherein data supplied by the assignment unit arestored in a memory.
 5. The apparatus according to claim 4, wherein saidmemory is a nonvolatile memory.
 6. The apparatus according to claim 1,wherein the transmitters emit their signal in a certain sequence.
 7. Theapparatus according to claim 1, wherein signals emitted by a transmitterare characteristic of the particular transmitter.
 8. The apparatusaccording to claim 1, wherein the transmitters and the receiverscomprise ultrasonic devices.
 9. The apparatus according to claim 1,wherein a coordinates zero point is defined with respect to which theposition of the tool is determined.
 10. The apparatus according to claim1, wherein proper functional operation of a tool is detected.
 11. Theapparatus according to claim 10, wherein information regarding operationof the tool is also filed in a memory.
 12. The apparatus according toclaim 1, wherein tool position determination takes place according toone of i) set time intervals, ii) as a function of an assembly lineposition, and iii) after a targeted activation.
 13. Apparatus forassigning a tool to a workpiece conveyed on an assembly line comprising:at least one receiver arranged in the area of an assembly line; atransmitter arranged on the tool; an analyzing unit which determines aposition of the tool relative to a defined fixed reference point, basedon transit times of signals transmitted by said transmitter and receivedby said at least one receiver; a device which indicates positions ofworkpieces conveyed on the assembly line, relative to the assembly line;and an assignment unit which assigns a tool or a tool position to aworkpiece, based on a comparison of the determined position of the tooland the workpiece positions indicated by said indicating device.
 14. Theapparatus according to claim 13, wherein: the at least one receivercomprises a plurality of receivers; and positions of the receivers areknown.
 15. The apparatus according to claim 13, wherein the at least onereceiver moves along together with an assigned workpiece on the assemblyline.
 16. The apparatus according to claim 13, wherein data supplied bythe assignment unit are stored in a memory.
 17. The apparatus accordingto claim 16, wherein said memory is a nonvolatile memory.
 18. Apparatusaccording to claim 13, comprising a plurality of transmitters, oneassigned to each of a plurality of tools, wherein the transmitters emittheir signals in a defined sequence.
 19. The apparatus according toclaim 18, wherein signals emitted by a particular transmitter arecharacteristic of that particular transmitter.
 20. The apparatusaccording to claim 18, wherein the transmitter and receiver compriseultrasonic devices.
 21. The apparatus according to claim 13, wherein acoordinate zero point is defined with respect to which the position of aparticular tool is determined.
 22. The apparatus according to claim 13,wherein proper functional operation of the tool is detected.
 23. Theapparatus according to claim 22, wherein information regarding operationof the tool is stored in a data memory.
 24. The apparatus according toclaim 13, wherein tool position determination takes place according toone of i) set time intervals, ii) as a function of an assembly lineposition, and iii) after a targeted activation.
 25. A method forcoordinating positioning of a tool and a workpiece, comprising: a firstsensor continuously determining time-related position of the toolrelative to a defined fixed zero point; continuously monitoringtime-related position of the workpiece relative to a reference system,based on position information from a source of position informationwhich is different from said first sensor; comparing the determinedtime-related position of the tool with the monitored time-relatedposition of the workpiece; and generating a time-related assignment ofthe tool to the workpiece, based on a result of said comparing.
 26. Themethod according to claim 25, wherein said generating step comprisesdetermining whether the tool has been guided to a particular position ofthe workpiece.
 27. The method according to claim 25, wherein: saidreference system comprises an assembly line along which the workpiece ismoved, and said source of position information is a master controlsystem for said assembly line; and said time-related position of saidtool comprises an absolute position in space.
 28. The method accordingto claim 26, further comprising: monitoring operation of said tool; andbased on said time-related assignment of said tool to said workpiece,and on said monitored operation of said tool, determining whether adefined assembly operation has been performed on said workpiece.